The data on recovery of infectious virus must be interpreted in relation to the amount of antibody in the test material. Table 4 shows results of HI tests on the serums and tissue extracts from experiment 1, and table 2, column 4, shows HI tests on serums from experiment 2. To evaluate the content of nonspecific inhibitors as well as of antibody, the tests on tissue extracts were made on the untreated material and on the same suspension after treatment with RDE; the inhibition of HA by the untreated suspension represents the effect of both inhibitor and antibody, while inhibition by the RDE-treated material represents antibody alone. During the peak phase of virus growth, HI tests were often not possible because of hemagglutinin in the tissue suspensions,fpar-ticularly those treated with RDE. Antibody appeared in serum, at the level of testing, on the 10th day of infection, and rose progressively through the 20th to 30th day, generally reaching titers of 1:1600 to 1:6400. Antibody in tissues was readily demonstrable after the 14th day, with titers in general agreement with that expected by their content of blood.

Table 4. Ha Inhibitors In Tissue Suspensions Obtained At Intervals After Inoculation Of Newborns: Experiment 1

*HI titer of serum expressed per 0.2 ml. of serum; titers of all other tissues expressed per 0.2 ml. of 10 percent suspension. †NT - No test because of HA by the tissue suspension.

Table 5. Representative Titrations Of Parotid Tumor Suspensions By Map And Tissue-Culture Tests

*Titers expressed per 0.2 ml. of serum and per 0.2 ml. of RDE-treated 10 percent tumor suspension.

† Results of 35-day MAP tests and mouse embryo tissue cultures observed for 30 days.

‡ Numerator = number of mice developing HI antibody. Denominator = number of mice inoculated.

§ Numerator = number of tissue-culture tubes demonstrating cytopathlc effects and/or hemagglutinin. Denominator = number of tubes observed.

Nonspecific inhibitor was found in salivary glands in high titer, which was anticipated from the mucoprotein nature of the erythrocyte receptors necessary for polyoma HA (6).

Detection and quantitation of virus in tissues taken late in infection were hampered by the high level of antibody in the tissue suspension. Whereas titrations of tissue extracts taken early in infection gave sharp titration endpoints in the MAP test, the late suspensions gave irregular antibody response over a wide dilution range. Occasionally parotid tumor suspensions gave prozones in MAP or tissue-culture titrations, presumably due to reactivation by dilution. Table 5 shows results of representative titrations of parotid tumor suspensions illustrating these points.

It should be noted that in other experiments we have twice encountered parotid tumor suspensions which gave no evidence of infectivity when titered in MAP and mouse embryo tissue-culture tests, but which yielded specific hemagglutinin and virus when the tumor tissue was grown in explant type culture in roller tubes.